// SCP协议实现（Phase 8）
// 参考OpenSSH scp.c源码

use crate::vfs::open_flags::OpenFlags;
use crate::vfs::{VfsBackend, VfsStat};
use anyhow::{anyhow, Result};
use log::{debug, info, warn};
use std::io::{BufRead, Read, Write};
use std::path::{Path, PathBuf};

/// SCP Handler（参考OpenSSH scp.c）
pub struct ScpHandler {
    pub root_dir: PathBuf,
    mode: ScpMode,
    recursive: bool,
    preserve_times: bool,
    pub vfs: Box<dyn VfsBackend>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ScpMode {
    Source,      // scp -f（发送文件）
    Destination, // scp -t（接收文件）
}

impl ScpHandler {
    pub fn new(root_dir: PathBuf, vfs: Box<dyn VfsBackend>) -> Self {
        Self {
            root_dir,
            mode: ScpMode::Destination,
            recursive: false,
            preserve_times: false,
            vfs,
        }
    }

    /// 解析SCP命令（参考OpenSSH scp.c: parse_command()）
    pub fn parse_scp_command(command: &str, vfs: Box<dyn VfsBackend>) -> Result<Self> {
        let parts: Vec<&str> = command.split_whitespace().collect();

        if parts.len() < 2 || parts[0] != "scp" {
            return Err(anyhow!("Invalid SCP command: {}", command));
        }

        let mut handler = ScpHandler::new(PathBuf::from("/tmp"), vfs);

        for part in &parts[1..] {
            match part {
                &"-f" => handler.mode = ScpMode::Source,
                &"-t" => handler.mode = ScpMode::Destination,
                &"-r" => handler.recursive = true,
                &"-p" => handler.preserve_times = true,
                path if !path.starts_with('-') => {
                    handler.root_dir = PathBuf::from(path);
                }
                _ => warn!("Unknown SCP flag: {}", part),
            }
        }

        Ok(handler)
    }

    /// 处理SCP传输（参考OpenSSH scp.c: source() / sink()）
    pub fn handle_scp(&mut self, channel: &mut dyn ReadWrite) -> Result<()> {
        match self.mode {
            ScpMode::Source => self.handle_source_mode(channel),
            ScpMode::Destination => self.handle_destination_mode(channel),
        }
    }

    /// SCP Source Mode（scp -f，发送文件）
    fn handle_source_mode(&self, channel: &mut dyn ReadWrite) -> Result<()> {
        info!(
            "SCP source mode: sending files from {}",
            self.root_dir.display()
        );

        let full_path = self.resolve_path(&self.root_dir.to_string_lossy())?;
        let stat = self
            .vfs
            .stat(&full_path)
            .map_err(|e| anyhow!("stat error: {}", e))?;

        if stat.is_dir {
            if !self.recursive {
                return Err(anyhow!("Directory detected but -r flag not specified"));
            }
            self.send_directory(channel, &full_path)?;
        } else {
            self.send_file(channel, &full_path)?;
        }

        Ok(())
    }

    /// SCP Destination Mode（scp -t，接收文件）
    fn handle_destination_mode(&mut self, channel: &mut dyn ReadWrite) -> Result<()> {
        info!(
            "SCP destination mode: receiving files to {}",
            self.root_dir.display()
        );

        channel.write_all(&[0])?;
        channel.flush()?;

        let mut buffer = String::new();

        loop {
            buffer.clear();

            let mut reader = std::io::BufReader::new(&mut *channel);
            match reader.read_line(&mut buffer)? {
                0 => break,
                _ => {
                    let command = buffer.trim();
                    debug!("SCP command: {}", command);

                    match command.chars().next() {
                        Some('C') => self.handle_file_command(channel, command)?,
                        Some('D') => self.handle_directory_command(channel, command)?,
                        Some('E') => self.handle_end_directory(channel)?,
                        Some('T') => self.handle_time_command(channel, command)?,
                        Some('\0') => {
                            continue;
                        }
                        _ => {
                            warn!("Unknown SCP command: {}", command);
                            self.send_error(channel, &format!("Unknown command: {}", command))?;
                        }
                    }
                }
            }
        }

        Ok(())
    }

    /// 发送文件（参考OpenSSH scp.c: source()）
    fn send_file(&self, channel: &mut dyn ReadWrite, path: &Path) -> Result<()> {
        let stat = self
            .vfs
            .stat(path)
            .map_err(|e| anyhow!("stat error: {}", e))?;
        let size = stat.size;
        let filename = path.file_name().unwrap().to_string_lossy();

        let command = format!("C0644 {} {}\n", size, filename);
        channel.write_all(command.as_bytes())?;
        channel.flush()?;

        let mut ack = [0u8; 1];
        channel.read_exact(&mut ack)?;
        if ack[0] != 0 {
            return Err(anyhow!("SCP file command rejected"));
        }

        let flags = OpenFlags::new().read();
        let mut file = self
            .vfs
            .open_file(path, &flags)
            .map_err(|e| anyhow!("open error: {}", e))?;

        let mut buffer = vec![0u8; 8192];

        loop {
            let n = file
                .read(&mut buffer)
                .map_err(|e| anyhow!("read error: {}", e))?;
            if n == 0 {
                break;
            }
            channel.write_all(&buffer[..n])?;
        }

        channel.flush()?;

        channel.write_all(&[0])?;
        channel.flush()?;

        channel.read_exact(&mut ack)?;
        if ack[0] != 0 {
            return Err(anyhow!("SCP file transfer rejected"));
        }

        info!("SCP file sent: {} ({} bytes)", filename, size);
        Ok(())
    }

    /// 发送目录（参考OpenSSH scp.c: source()）
    fn send_directory(&self, channel: &mut dyn ReadWrite, path: &Path) -> Result<()> {
        let dirname = path.file_name().unwrap().to_string_lossy();

        let command = format!("D0755 0 {}\n", dirname);
        channel.write_all(command.as_bytes())?;
        channel.flush()?;

        let mut ack = [0u8; 1];
        channel.read_exact(&mut ack)?;
        if ack[0] != 0 {
            return Err(anyhow!("SCP directory command rejected"));
        }

        let entries = self
            .vfs
            .read_dir(path)
            .map_err(|e| anyhow!("read_dir error: {}", e))?;

        for entry in &entries {
            let entry_path = path.join(&entry.name);

            if entry.stat.is_dir {
                if self.recursive {
                    self.send_directory(channel, &entry_path)?;
                }
            } else {
                self.send_file(channel, &entry_path)?;
            }
        }

        channel.write_all("E\n".as_bytes())?;
        channel.flush()?;

        channel.read_exact(&mut ack)?;
        if ack[0] != 0 {
            return Err(anyhow!("SCP end directory rejected"));
        }

        info!("SCP directory sent: {}", dirname);
        Ok(())
    }

    /// 处理文件命令（C0644 size filename）
    fn handle_file_command(&self, channel: &mut dyn ReadWrite, command: &str) -> Result<()> {
        let parts: Vec<&str> = command.split_whitespace().collect();

        if parts.len() != 3 {
            return self.send_error(channel, "Invalid file command format");
        }

        let mode_str = parts[0].trim_start_matches('C');
        let size: u64 = parts[1].parse()?;
        let filename = parts[2];

        debug!(
            "SCP receive file: mode={}, size={}, name={}",
            mode_str, size, filename
        );

        if size > 1024 * 1024 * 1024 {
            return self.send_error(channel, "File too large (max 1GB)");
        }

        let full_path = self.resolve_path(filename)?;

        let flags = OpenFlags::new().write().create().truncate();
        let mut file = self
            .vfs
            .open_file(&full_path, &flags)
            .map_err(|e| anyhow!("open error: {}", e))?;

        channel.write_all(&[0])?;
        channel.flush()?;

        let mut buffer = vec![0u8; 8192];
        let mut remaining = size;

        while remaining > 0 {
            let to_read = std::cmp::min(buffer.len() as u64, remaining) as usize;
            let n = channel.read(&mut buffer[..to_read])?;
            if n == 0 {
                break;
            }
            file.write_all(&buffer[..n])
                .map_err(|e| anyhow!("write error: {}", e))?;
            remaining -= n as u64;
        }

        file.flush().map_err(|e| anyhow!("flush error: {}", e))?;

        // 设置文件权限
        let mode_int: u32 = mode_str.parse()?;
        if mode_int != 0 {
            let mut set_stat = VfsStat::new();
            set_stat.mode = mode_int;
            self.vfs
                .set_stat(&full_path, &set_stat)
                .map_err(|e| anyhow!("set_stat error: {}", e))?;
        }

        let mut ack = [0u8; 1];
        channel.read_exact(&mut ack)?;

        channel.write_all(&[0])?;
        channel.flush()?;

        info!("SCP file received: {} ({} bytes)", filename, size);
        Ok(())
    }

    /// 处理目录命令（D0755 0 dirname）
    fn handle_directory_command(&self, channel: &mut dyn ReadWrite, command: &str) -> Result<()> {
        let parts: Vec<&str> = command.split_whitespace().collect();

        if parts.len() != 3 {
            return self.send_error(channel, "Invalid directory command format");
        }

        if !self.recursive {
            return self.send_error(channel, "Recursive flag not specified");
        }

        let mode_str = parts[0].trim_start_matches('D');
        let dirname = parts[2];

        debug!("SCP receive directory: mode={}, name={}", mode_str, dirname);

        let full_path = self.resolve_path(dirname)?;

        let mode_int: u32 = mode_str.parse()?;
        self.vfs
            .create_dir_all(&full_path, mode_int)
            .map_err(|e| anyhow!("create_dir_all error: {}", e))?;

        channel.write_all(&[0])?;
        channel.flush()?;

        info!("SCP directory created: {}", dirname);
        Ok(())
    }

    /// 处理结束目录命令（E）
    fn handle_end_directory(&self, channel: &mut dyn ReadWrite) -> Result<()> {
        debug!("SCP end directory");

        channel.write_all(&[0])?;
        channel.flush()?;

        Ok(())
    }

    /// 处理时间命令（T mtime atime）
    fn handle_time_command(&self, channel: &mut dyn ReadWrite, command: &str) -> Result<()> {
        if !self.preserve_times {
            channel.write_all(&[0])?;
            channel.flush()?;
            return Ok(());
        }

        let parts: Vec<&str> = command.split_whitespace().collect();

        if parts.len() != 3 {
            return self.send_error(channel, "Invalid time command format");
        }

        let mtime_secs: i64 = parts[1].parse()?;
        let atime_secs: i64 = parts[2].parse()?;

        debug!("SCP set times: mtime={}, atime={}", mtime_secs, atime_secs);

        channel.write_all(&[0])?;
        channel.flush()?;

        Ok(())
    }

    /// 发送错误消息
    fn send_error(&self, channel: &mut dyn ReadWrite, message: &str) -> Result<()> {
        let error_msg = format!("{}\n", message);
        channel.write_all(error_msg.as_bytes())?;
        channel.flush()?;
        Err(anyhow!("SCP error: {}", message))
    }

    /// 路径解析（安全性检查）
    pub fn resolve_path(&self, path: &str) -> Result<PathBuf> {
        let full_path = self.root_dir.join(path);

        let canonical_path = self
            .vfs
            .real_path(&full_path)
            .map_err(|e| anyhow!("Path resolution error: {}", e))?;

        let root_canonical = self
            .vfs
            .real_path(&self.root_dir)
            .map_err(|e| anyhow!("Root path resolution error: {}", e))?;

        if !canonical_path.starts_with(&root_canonical) {
            return Err(anyhow!("Path traversal attempt detected"));
        }

        Ok(canonical_path)
    }
}

/// Read + Write trait组合（用于Channel）
pub trait ReadWrite: Read + Write {}
impl<T: Read + Write> ReadWrite for T {}

/// ⭐⭐⭐⭐⭐ Phase 8: Channel wrapper for SCP protocol
/// 实现 Read + Write traits，用于 ScpHandler 和 SSH channel 之间传递数据
pub struct ChannelReadWrite {
    input_buffer: Vec<u8>,
    output_buffer: Vec<u8>,
    input_pos: usize,
}

impl ChannelReadWrite {
    pub fn new(input_buffer: Vec<u8>) -> Self {
        Self {
            input_buffer,
            output_buffer: Vec::new(),
            input_pos: 0,
        }
    }

    pub fn feed_input(&mut self, data: &[u8]) {
        self.input_buffer.extend_from_slice(data);
    }

    pub fn drain_output(&mut self) -> Vec<u8> {
        let output = self.output_buffer.clone();
        self.output_buffer.clear();
        output
    }

    pub fn has_remaining_input(&self) -> bool {
        self.input_pos < self.input_buffer.len()
    }
}

impl Read for ChannelReadWrite {
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        let remaining = self.input_buffer.len() - self.input_pos;
        let to_read = std::cmp::min(buf.len(), remaining);
        
        if to_read == 0 {
            return Ok(0);
        }

        buf[..to_read].copy_from_slice(&self.input_buffer[self.input_pos..self.input_pos + to_read]);
        self.input_pos += to_read;
        
        Ok(to_read)
    }
}

impl Write for ChannelReadWrite {
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        self.output_buffer.extend_from_slice(buf);
        Ok(buf.len())
    }

    fn flush(&mut self) -> std::io::Result<()> {
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::vfs::local_fs::LocalFs;

    fn make_handler() -> ScpHandler {
        ScpHandler::new(PathBuf::from("/tmp"), Box::new(LocalFs::new()))
    }

    #[test]
    fn test_scp_command_parse() {
        let handler =
            ScpHandler::parse_scp_command("scp -t /tmp", Box::new(LocalFs::new())).unwrap();
        assert_eq!(handler.mode, ScpMode::Destination);
        assert_eq!(handler.root_dir, PathBuf::from("/tmp"));
    }

    #[test]
    fn test_scp_recursive_parse() {
        let handler =
            ScpHandler::parse_scp_command("scp -r -t /tmp", Box::new(LocalFs::new())).unwrap();
        assert!(handler.recursive);
    }

    #[test]
    fn test_scp_source_parse() {
        let handler =
            ScpHandler::parse_scp_command("scp -f /tmp", Box::new(LocalFs::new())).unwrap();
        assert_eq!(handler.mode, ScpMode::Source);
    }
}